The present invention relates generally to air-fuel mixture control systems for an internal combustion engine, and particularly to a closed-loop mixture control system using the sampling technique to minimize adversary effect caused by varying operating parameters of the engine.
In a closed-loop mixture control system, a sudden change of an engine operating parameter may introduce a certain degree of control oscillation due to the inherent time delay which is largely accounted for by the transport delay time of the engine from the injection of air-fuel mixture to the sensing of the exhaust composition. Integral control is usually conveniently employed for linearly varying the fuel quantity. However, due to the transport delay time the integral control keeps influencing the fuel quantity in the same direction although the reference point has been passed, resulting in a higher amplitude, lower frequency oscillation.